High velocity shaft seal

ABSTRACT

A power unit of the type comprising an internal combustion engine having a pair of opposed free pistons working in a common cylinder, a pair of pump units connected to the cylinder at opposite ends thereof, each pump unit comprising a pump piston coacting with a respective one of the engine pistons and working in a pump chamber, the engine cylinder providing inlet ports and exhaust ports communicating with respective inlet and exhaust manifolds for admitting combustion air to, and exhausting combustion gases from, the cylinder, the engine cylinder further providing first and second air compression spaces located respectively behind the engine pistons, each air compression space having a valve controlled air inlet and a valve controlled air outlet, and duct means connecting said air outlets with the inlet manifold wherein the air compression spaces are separated from the pump chambers by bulkheads providing cylindrical openings through which the pump pistons extend, each opening being formed with a drainage groove encircling the pump piston to provide a trap for leakage fluid, the grooves being connected by ducts to a float chamber having a float-controlled outlet, and means for biasing the float according to the average air pressure in said air compression spaces.

Waited States Patent [1 1 Fitzgerald Nov. 11, 1975 HlGl-l VELOCITY SHAFTSEAL [76] Inventor: William Maurice Bard Fitzgerald,

RR. No. 1, Claremont, Ontario. Canada Filed: Sept. 9, .1974

Appl. 710.: 504,722

Related U.S. Application Data [62] Division of Ser. No. 305,453, Nov.10, 1972 Pat. No.

[52] US. Cl. 4l7/364; 417/380; 92/86 [51] Int. Cl. F04B 17/00 [58] Fieldof Search 123/46 R; 417/364, 380; 92/86, 86.5

[56] References Cited UNITED STATES PATENTS 1545.930 7/1925 Vincent92/86 3.119.230 1/1964 Kosoff 123/46 X 3,177,861 4/1965 Quillian, Jr.92/36 X 3.229.900 1/1966 McCrory et al.. 92/865 3329133 7/1967 Panaard417/364 X 3,363,609 1/1968 Cadiou 417/364 X Primary E.\'uminerCharles.1. Myhre Assistant E.\'aminerWilliam C. Anderson [57] ABSTRACT A powerunit of the type comprising an internal combustion engine having a pairof opposed free pistons working in a common cylinder, a pair of pumpunits connected to the cylinder at opposite ends thereof, each pump unitcomprising a pump piston coacting with a respective one of the enginepistons and working in a pump chamber, the engine cylinder providinginlet ports and exhaust ports communicating with respective inlet andexhaust manifolds for admitting combustion air to, and exhaustingcombustion gases from, the cylinder, the engine cylinder furtherproviding first and second air compression spaces located respectivelybehind the engine pistons, each air compression space having a valvecontrolled air inlet and a valve controlled air outlet, and duct meansconnecting said air outlets with the inlet manifold wherein the aircompression spaces are separated from the pump chambers by bulkheadsproviding cylindrical openings through which the pump pistons extend,each opening being formed with a drainage groove encircling the pumppiston to provide a trap for leakage fluid, the grooves being connectedby ducts to a float chamber having a float-controlled outlet, and meansfor biasing the float according to the average air pressure in said aircompression spaces.

2 Claims, 44 Drawing Figures US. Patent Nov. 11, 1975 Sheet 1 of 14 US.Patent Nov. 11,1975 Sheet20f14 3,918,851

l-li-ln US. Patent Nov. 11, 1975 Sheet 3 of 14 3,918,851

FROM 114R FIG.7

US. Patent Nov. 11, 1975 Sheet4 of 14 3,918,851

'IIIHIII 237 240 287 1041 104R FIG. 20

205 FIG. 18

US. Patent Nov. 11, 1975 Sheet 6 of 14 3,918,851

FIG. 22

276 268 272 287 FIG. 23

US. Patent N0v.11, 1975 Sheet7of14 3,918,851

l l I 298 FIG. 30

US. Patent Nov. 11, 1975 Sheet 8 (14 3,918,851

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@Nm wwm Sheet 9 of 14 US. Patent 1 Nov. 11, 1975 31 FIG. 29 O 0 (3-317(4 350 J U 1 \HJIIH Hm I 3O2\ 32g 322 H}? nu g) 336 3 3 1111 FIG. 28 G)US. Patent Nov. 11, 1975 Sheet 10 of 14 3,918,851

US. Patent Nov. 11, 1975 Sheet110f14 3,918,851

Eli-iii US. Patent Nov. 11, 1975 Sheet 12 of 14 3,918,851

FIG. 36

III I FIG. 38

FIG. 37

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US. Pamm Nov. 11,1975 Sheet 13 0114 3,18,851

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El4 El? FIG-41 b HIGH VELOCITY SHAFT SEAL CROSS REFERENCE TO RELATEDAPPLICATION This application is a divisional of my copending applicationSer. No. 305,453, filed Nov. 10 and now US. Pat. 3841797, 1972 relatingto Power Units.

BACKGROUND OF THE INVENTION This invention relates to a shaft sealarrangement, more particularly for engines, compressors and pumps, suchas for example the free piston engine described in my copendingapplication Ser. No. 305,453 identified above.

Hitherto, shaft seals for use in engines, compressors and pumps haverequired a sealing ring, piston ring or the like having a minimalclearance with the cylinder wall. When the clearance is very small, heatis generated through friction in the lubricant which lines the cylinderwall, and this generation of heat limits the speed at which the seal canoperate satisfactorily. Some systems have dispensed with the use ofsealing rings, but in these cases lubricating oil leaks very rapidlyaway.

It is an object of the present invention to avoid these disadvantages bypermitting a large clearance between the relatively movable surfaces,while ensuring that any oil leakage is returned to a sump tank so as notto be lost when the engine compressor or pump is standing still.

SUMMARY OF THE INVENTION As applied to a power unit of the typedescribed in the above mentioned patent application, wherein aircompression spaces are separated from the pump chambers by bulkheadsproviding cylindrical openings through which the pump pistons extend,each opening is formed with a drainage groove encircling the pump pistonto provide a trap for leakage fluid, the grooves being connected byducts to a float chamber having a float control outlet, and means forbiasing the float according to the average air pressure in the aircompression spaces. Preferably, the float chamber provides an air spaceabove the float, which air space is connected to the air compressionspaces by a duct having a flow restricting orifice.

One embodiment of the invention, as applied to a power unit andtransmission system for a wheeled vehicle, will now be described by wayof example with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section taken through the axis of the powerunit;

I FIG. 2 is a fragmentary top plan view of the power unit;

FIG. 3 is a section on line 3-3 in FIG. 1;

FIG. 4 is a section on line 44 in FIG. 1;

FIG. 5 is a section on line 55 in FIG. 1;

FIG. 6 is a section on line 6-6 in FIG. 1;

FIG. 7 is a section on line 7-7 in FIG. 1;

FIG. 8 is a section on line 8-8 in FIG. 6

FIG. 17 shows a section on line 17-17 in FIG. 2;

FIG. 18 shows a central vertical section through the fuel injector ofthe unit, the section being on line 18-18 of FIG. 19;

FIG. 19 is a partly sectioned side elevation of the fuel injector;

FIG. 20 is a section on line 2020 in FIG. 18;

FIG. 21 is an unsectioned end view of FIG. 18;

FIG. 22 shows the outside of a spool valve element;

FIG. 23 is a section on line 2323 in FIG. 18;

FIG. 24 is a section on line 24-24 in FIG. 18;

FIG. 25 is a section on line 2525 in FIG. 18;

FIG. 26 is a sectional view of a valve connector adapted to be used withthe fuel injector;

FIG. 27 is a part-sectional plan view of a control gear for starting andstopping the power unit;

FIG. 28 is a part elevation on line 2828 in FIG. 27;

FIG. 29 is an unbroken plan view of the control gear;

FIG. 30 is an end elevation of the control gear viewed from the left inFIG. 27 with certain parts removed;

FIG. 31 is a sectional plan view on line 3l31 in FIG. 27;

FIG. 32 is a fragmentary view in the direction of arrow 32 in FIG. 27with certain parts removed;

FIG. 33 is a part elevation showing the end view of a solenoid;

FIG. 34 is a partly broken away side elevation of a reversible hydraulicmotor adapted for use with the power unit;

FIG. 35 is a section on line 35-35 in FIG. 34;

FIGS. 36 and 37 illustrate details of a planet gear bearing fromopposite sides thereof;

FIG. 38 is a section on line 3838 in FIG. 37;

FIG. 39 is a section on line 39-39 in FIG. 34 with certain partsremoved, showing a planet gear without details of its teeth;

FIG. 40 is a schematic view of a gear wheel of the motor; and

FIGS. 41a and 41b are a schematic overall representation of the completepower unit and ancillary equipment;

FIG. 42 is a section on line 42-42 in FIG. 41;

FIG. 43 is a section on line 4343 in FIG. 41.

THE POWER UNIT General The power unit comprises an internal combustionengine having a pair of opposed free pistons, a pair of pump units thepistons of which coact with the engine pistons, a pair of constantdisplacement hydraulic accumulators into which pressurized hydraulicfluid is pumped in accordance with the expansion strokes of the enginepistons, inlet ports and exhaust ports under the control of the pistonsfor admitting combustion air to, and exhausting combustion gases from,the engine, and valve operated fuel injection means actuated inaccordance with the cyclical movements of the pistons to control theinjection of fuel into the engine. The power output from the engine is aflow of pressurized hydraulic fluid, which in the present example isdelivered from a pair of smoothing accumulators and used to drivehydraulic motors.

Arrangement and Mechanical Construction The mechanical construction ofthe power unit itself, and certain details of such construction, areillustrated in FIGS. 1 to 17, of which FIG. 1 best illustrates thegeneral arrangement of the unit. Reference will now be made to thesefigures in particular.

At the heart of the power unit is a compressionignition enginecomprising a single, water-cooled cylinder 101 having a ring of airinlet ports 102 and a ring of exhaust ports 103, and a pair of opposedfree pistons I04L and 104R of equal mass. The piston 104L and 104R arefree to reciprocate within the cylinder 101, and the overall designincludes means to ensure that the pistons always move simultaneously inopposite directions and are also disposed symmetrically on oppositesides of a central position denoted by line 44 in FIG. 1. A fuelinjector 200 is bolted to the cylinder 101 at the central position, sothat its nozzle 201 is positioned to inject fuel into the space betweenthe opposed pistons at appropriate times, as will be describedhereinafter.

Each end of the cylinder 101 is bolted to a respective one of twosimilar hydraulic accumulator-pump assemblies 105, 106. The assembly 105(which will be described in detail, the assembly 106 being identical inconstruction) comprises a pump unit 107, a first, constant displacementhydraulic accumulator 108, and a second, high pressure or smoothinghydraulic accumulator 109, the assembly having a casing structureincluding a bulkhead 110 which is bolted to the cylinder end by bolts111.

The pump unit 107 provides an internal oil-filled space or pump chamber112, and houses a composite cylindrical or pump piston 113 which is areasonably leak-free sliding fit in the bulkhead 110. The combinedeffects of the momentum of the pump piston 113, and the pressure in thepump chamber 112, ensure that the pump piston 113 is always pressedagainst the engine piston 104L.

A groove 114 in the bulkhead allows oil leaking along the outer wall ofthe pump piston 113 to pass into a pipe 177 (FIG. 5) which conveys it toa float chamber 178. Within the float chamber 178 is a float 179, whichon rising uncovers a drain hole 180 leading back to a vented reservoir514, (FIG. 41) via a pipe X. A tube, 181 leading via a restrictor 182 toa hole 183 in the bulkhead 110 gives access to the air compression space117. A valve 184 may be used to open or close access to the aircompression space so that air may be extracted therefrom in order toform a vacuum with which to suck the pistons 104L and 104R into theirstarting position. The float 179 and drain hole 180 are preferably sodimensioned that the float will rise before its total submersion underany conditions of average pressure that may exist in float chamber 178.In any case after the engine is brought to rest, pressure in the floatchamber 178 will fall so that oil leaking along the outer wall of thepump piston 113 will flow into it, and when the level is sufficientlyhigh the float will rise and allow the leaking oil to flow down into avented reservoir 514 (FIG. 41).

The pump piston 113 is in the form of a hollow ram which defines aninternal oil space and contains a heavy plunger 115 which is free tomove back to a retaining screw 118, and forward to cover an oil flowrestrictor 116 at the inner end of the ram; it will move in this mannerunder the impetus of its own inertia, pressing against the oil flowrestrictor 116 at the inner end when the piston 104L is acceleratingduring the first part of its outward stroke and decelerating during thelast part of its re-compression stroke. The ram will be pressed againstthe retaining screw 118 during the last part of its expansion stroke andthe first part of its recompression stroke. The restrictor 116 allows acontrolled quantity of oil to pass into a hole shown by dotted lines 164and on through a number of holes 165 into a groove 166 round the piston104L for cylinder wall lubrication where the piston slides. A spring118A contained within the retaining screw 118 urges the solid rodinwards to close the restrictor 116 when the engine is at rest so thatoil cannot escape through the restrictor at this time.

The first, constant displacement accumulator 108 comprises a domedcasing providing a stepped cylindrical internal surface 120. The domedcasing houses a downwardly projecting cylindrical sleeve 121 in which apiston 122 is free to move axially up or down. The lower portion of saidstepped cylindrical surface constitutes a cylinder communicating withthe pump chamber I12 and locating a leak-free piston 123 which is freeto move axially up or down. The pistons 122 and 123 define within thefirst accumulator a space 124 of variable volume which contains nitrogenor other gas under pressure. A second, oil-filled space 125 is situatedabove piston 122, to or from which oil may be admitted or withdrawn viaa port 126 in the dome 127 of the casing. The piston 123 is formed witha flange 128 which is adapted to come to rest against a step 129 of saidstepped cylindrical surface 120 and to abut against the lower end of thesleeve 121, for limiting the downward and upward movements of the piston123. Thus the piston 123 is constrained to move between lower and upperlimit positions which determine the minimum and maximum charge levels ofthe accumulator, respectively. A sump 130 is formed by the piston 123,in which any oil that may leak into the space 124 will collect and fromwhich it may be withdrawn via a duct 131. This duct also serves forrecharging the gas space 124 and to adjust its pressure; a suitablevalve would normally be fitted into the duct 131.

It is necessary to ensure rapid establishment of inlet oil flow into thepump chamber 112 once the chamber pressure falls as the result of theflange 128 of accumulator piston 123 coming to rest against the step129, while the pump piston 113 still continues its outward stroke. Forthis purpose, an inlet oil assembly 132 is provided to control the flowof oil through a springloaded plate valve 133. In this assembly: (1) themass of the moving element of the valve 133 -is kept reasonably low; (2)a diaphragm 132D, backed by a suitable gas such as nitrogen, containedin a space 132G, keeps to a minimum the mass of oil that must beaccelerated on each cycle; (3) the cross-sectional area of the oil,perpendicular to its direction of flow, is large so as to keep the oilvelocity 10w; (4) the inlet oil in space 132E is raised to a fairly highpressure, which for example might in a particular instance be pounds persquare inch. When the pump piston 113 moves inwards into the pumpchamber 112, the first accumulator is first charged to its full capacityand then oil is forced via a second automatic spring-loaded plate valve134 into the second hydraulic accumulator 109. The details ofconstruction of the second automatic plate valve 134, which isessentially a high speed one-way valve, are illustrated in FIGS. 9 to13. The first automatic plate valve may be similarly constructed. Asillustrated in FIGS. 9 to 13, the valve comprises essentially astationary valve element in the form of a grid, and a thin plate whichis formed as a complementary grid, the thin plate being urged intocontact with the stationary valve element by an array of compressionsprings. When the valve is closed, the grid elements of the thin plateclose off the spaces between the elements of the stationary valveelement; when the thin plate is displaced by a small amount, however,these spaces are opened simultaneously. Thus the valve openssubstantially to its maximum extent with a minimal displacement of themovable valve element.

The second hydraulic accumulator 109, best shown in FIGv 6, s connectedto the oil delivery opening of the pump chamber 112, which opening iscontrolled by the automatic one-way valve 134. The accumulator 109comprises a domed casing housing a cylindrical sleeve 135 within which apiston 136 is free to slide axially up or down. The piston 136 defineswithin the sleeve 135 a space 137, which is filled with nitrogen orother suitable gas under pressure. A vent 138 (FIG. 17) for filling thespace 137 leads into the clearance space that exists between thecylindrical sleeve 135 and the casing 109. When the pump piston 113moves inwards it first charges the constant displacement recompressionaccumulator 108 by forcing the piston 123 up until the latter is broughtto rest against the lower end of the sleeve 121, and oil then passesfrom the chamber 112 via the one-way valve 134 into an oil space 139 ofthe second accumulator 109, which has an outlet port 140 from which thepressurized oil is supplied to the hydraulic load circuit.

Communicating with the air compression space 117 behind each of theengine pistons 104L and 104R is a thin springloaded air inlet valve 141fitted in an entrance 142, and a thin spring-loaded air delivery valve143 fitted in an outlet 144; these valves admit air into the compressionspaces 117 on the compression strokes of the pistons, and permit egressof air from the compression spaces on the expansion strokes of thepistons, respectively. The entrances 142 may be connected by flexiblemetal tubing to an air inlet filter, atmospheric air being filtered andadmitted through the valves. In the preferred embodiment illustrated inthe drawings, however, the entrances 142 are connected by a duct 145 tothe outlet of an air compressor 146. The duct 145 may also include anair cooler. The compressed air from the outlets 144, after cooling ifnecessary, is conveyed via ducts 147 (shown broken away in FIG. 1) to aninlet 148 communicating via an air inlet manifold 149 with the inletports 102 of the engine cylinder (see FIG. 3). The inlet ports 102 andthe ends of the air inlet manifold 149 are preferably shaped so as toinduce a swirling motion of the incoming air, for example as indicatedby the arrows of FIG. 3. In the present embodiment the depth of thechannel perpendicular to the cross sectional plane of FIG. 3, tapersfrom the inlet 148 to the ends of the manifold so as to-promoteapproximately the same air velocity throughout the manifold. Thisproduces two elongated air flow vortices in the engine cylinder, asindicated in FIG. 3. Fuel is injected from the injection nozzle 201, asindicated in FIG. 4, at about maximum compression.

Additional openings 150 may be provided in the wall of the enginecylinder 101. These openings, one of which is presently shown closed bya cover 151, may be used to apply compressed air for moving the pistonsapart if necessary, (when the engine is inoperative,) or to connect apressure gauge for research or experimental purposes, or to provide analternative means for fuel injection or full injection timing, or toadmit air when the pistons are being set in a starting position, as willbe explained hereinafter.

The engine exhaust system comprises a casing 152 providing a storagespace 153, which communicates with the exhaust ports 103 via a manifoldor passage 154 in the engine cylinder. A casing 155 bolted to the bottomend of the casing 152 provides an internal space 156 which communicateswith the stora e space 153 by way of ports 157. An intake tube 158connected to the upper end of the casing 155 projects upwards inalignment with the passage 154, the latter being spaced from the end ofthe intake tube. The casing 155 also provides an internal cylinderportion containing a spool valve 160, which is biassed upwardly by aspring shown diagrammatically at 159. In operation of the engine, whenthe exhaust ports 103 are uncovered by the piston 104R towards the endof a compression stroke, the products of combustion enter the storagespace 153 and impinge upon the intake tube 158. If the kinetic energy ofthe exhaust gases is relatively low, the spool valve 160 remains in itsupper position and the exhaust gases pass to a silencer (not shown) viaducting 161. However, if the kinetic energy of the exhaust gases issufficiently high, the spool valve 160 is displaced downwards to coverthe ports 157; in this case the gases in the storage space 153, being ofincreased pressure, pass through a duct 162 to an exhaust turbine, thelatter being combined with the air compressor 146. The spent gases arefinally exhausted via a pipe 163 and a silencer (not shown).

Each of the engine pistons is formed with a circumferential annulargroove 169 having bevelled sides, into which a plunger 170 having acorrespondingly bevelled end may be forced, in order to lock the pistonsagainst movement when the engine is not running. In FIG. 1 the plungers170 are shown neither fully in nor fully out, but are shown forillustration in an intermediate position. Each plunger 170 is normallyheld out of the respective annular groove 169 when the engine isrunning, by a U-spring 171 which engages a grooved portion 172 of theplunger. When required, the plungers 170 are passed into theiroperative, pistonholding positions by actuating pistons 173; the latterare slidable in cylinders 174 and are actuated by hydraulic pressureapplied via oil connections 175 when the pistons 104L and 104R are nearthe ends of their expansion strokes. The plungers 170 hold the pistons104L and 104R approximately in the position shown in FIG. 1, against theforces exerted by the rams 113, the latter being urged by hydraulicpressure from the accumulators 108. The forward speed of each actuatingpiston 173 is controlled by an orifice in a plate valve 167; the partsare designed to permit comparatively free flow in the reverse directionwhen the engine is being started. A light spring 168 holds the valveplate normally forward.

The output of the engine is a flow of pressurized liquid. The amplitudeand frequency at which the engine pistons 104L and 104R reciprocate arevariable, depending upon the power that is being'developed. Thepositions at which the pistons momentarily stop at the end of thecompression stroke are largely determined by the initial momentum of thepistons and the pressure of the initial cylinder air charge. Thepositions at which the pistons momentarily stop at the end of theexpansion stroke are determined by the momentum that they have gainedfrom the energy of combustion, the cyclic range of oil pressures, andthe rate of flow of the hydraulic liquid. To maintain an approximatelyconstant compression ratio in the engine cylinder 101, more energy willbe required at high intake air pressures than at low intake airpressures; however, the same invariable volume of oil, determined by thestroke of each piston 123 of the constant displacement hydraulicaccumulators, as it reciprocates between the limits of its movement,will always be set aside for the return strokes of the engine pistons.Therefore the average pressure of this oil must be altered as requiredin accordance with the pressure of the intake air. It can easily beshown that when the average oil pressure in each of the constantdisplacement accumulators 108 is low, (to accommodate low intake airpressure,) the average compression speeds of the pistons 104L and 104Rwill also be low and the time taken to effect the compression strokeswill be correspondingly long. Conversely, when the average oil pressurein each of the constant displacement accumulators 108 is high, thespeeds of the pistons 104L and 104R will be high, so that the time toeffect the compression strokes will be correspondingly short. The samefactors apply to the speeds of the pistons on the expansion strokes, sothat the time to complete the strokes will be an inverse function of theenergy developed. The net result is that the rate of reciprocation ofthe engine pistons will be low at low power outputs and high at highpower outputs.

Power Unit Operation With the stop plungers 170 completely retracted,the engine pistons 104L and 104R and the pump pistons 113 are initiallyin the positions shown in FIG. 1 with the engine pistons moving towardsone another; the engine pistons 104L and 104R and the pump pistons 113together have sufficient momentum to give an air compression ratio of,say :1, or higher. Subsequently to this initial stage the oil inletplate valves 133 open. The air inlet valves 141 are already open and theair delivery valves 143 are closed, so that air enters the aircompression spaces in the engine cylinder lying between the enginepistons and the bulkheads 110. The pump pistons 113 also move out fromthe pump chambers 112, under the action of their momentum and thepressurized fluid passing through the inlet oil valves 133. At about theposition when the momentum of the pump pistons, together with themomentum of the engine pistons 104L and 104R, is spent in compressingthe air charge in the cylinder 101, fuel is injected into the cylinderby the fuel injector 200; the gas charge temperature and the relativepressure then rises and the engine pistons are caused to accelerate awayfrom each other, performing their working or expansion stroke.

The one-way plate valves 133 then close and the pump pistons 113 areforced inwards by pistons 104, first to charge the accumulators 108,which are adjusted so as to yield at less pressure than the pistons 136of the variable displacement accumulators 109. When the pistons 123 havecompleted their strokes, which are terminated by the abutment of thesepistons against the lower ends of the sleeves 121, the pressure in thepump chambers 112 continues to rise and the one-way plate valves 134open against the pressure in the oil spaces 139 of the variabledisplacement accumulators 109. During normal running of the unit, thepistons 136 are at a higher postion than that shown in the drawings, de

pending upon the pressure required. The surge ofoil on each pumpingstroke, after first displacing the pistons 123 in the constantdisplacement accumulators 108, is absorbed in urging the pistons 136inwards against the pressure of gas in the gas spaces 137, but the oilis continually leaving at a more moderate velocity through the outletports 140. When the momentum of the engine pistons 104L and 104R isspent, the pistons stop and the high speed plate valves 134 close. Thepistons 123 are subjected to pressure from the gas above them and stillmaintain a substantial pressure on the oil in the pump chambers 112;this pump chamber pressure acts on the pump pistons 113 and acceleratesthe engine pistons 104L and 104R back along another compression strokeas already described. During the time in which the pistons 104L and 104Rare moving outwards on the expansion stroke, the pressure in the aircompression spaces 117 is increasing, and when this pressure exceeds thepressure above the air delivery valves 143, the latter open to admitthis air charge.

Outlets 176 from the pump chambers 112 are connected to pipes 5151s,515R (FIG. 41), as will be described hereinafter. A peripheral groove119 is incorporated in the piston rod bearing of each bulkhead as partofa means to ensure synchronisation of the engine pistons 104L and 104R,as will also be explained hereinafter. By these means continuous runningof the engine is achieved.

THE FUEL INJECTOR General The fuel injector 200 of FIG. 1 comprisesinjection means for injecting predetermined quantities of fuel into theengine cylinder, and actuator means for actuating the injection means inaccordance with the air pressure within the engine cylinder so as toensure that the predetermined quantities of fuel are injected into thecylinder at appropriate times in relation to the combustion cycle of theengine.

The injection means comprises, basically, a fuel injection nozzle, avalve controlled supply chamber lo cated behind the injection nozzle,means for admitting fuel to the fuel supply chamber, and a fuel pistonactuated by said actuator means to compress the fuel in the supplychamber and to expel the fuel therefrom to the engine cylinder via theinjection nozzle. The actuator means includes a spring-loaded shuttlevalve arranged to move towards one or other of two limit positions inaccordance with the gas pressure in the engine cylin der, and means forsupplying pressurized hydraulic fluid to actuate the fuel piston inaccordance with the position of the shuttle valve; the pressurizedhydraulic fluid is fed from a chamber housing a free piston which isurged in a direction to expel hydraulic fluid from the chamber,expulsion of fluid from the chamber being controlled by the shuttlevalve, which is arranged to cover and uncover a port leading to thechamber.

Arrangement and Mechanical Construction The fuel injector is illustratedin detail in FIGS. 18 to 26 of the drawings, of which FIG. 18 best showsthe interrelationship ofits working parts. Reference will now be made tothese figures in particular.

In FIG. 18 is shown a portion of the engine cylinder 101, and portionsof the engine pistons 104L and 104R which define a combustion space S inthe engine cylinder into which fuel is injected by the feel injector.The

fuel injector itself is incorporated in a metal body 202, which ismachined to provide a number of internal passages and bores ashereinafter described, and which houses the essential elements of theinjection means and the actuator means referred to above.

The metal body 202 is formed with a stepped cylindrical bore 203, at theupper end of which is an assembly consisting of the injection nozzleitself 201, a spring-loaded valve 204 having a valve seat 205, a spacerring 206, and another spacer ring 205A which may be of relatively softmetal such as mild steel, those parts being clamped and retained inposition by an adaptor 207 which is screwed into the threaded upper endof the cylindrical bore 203. The adaptor 207 is located in a passage inthe wall of the engine cylinder 101, to which the fuel injector body 202is suitably connected, a sealing ring 208 being located so as to preventleakage of gases from the engine cylinder.

Located within the cylindrical bore 203 is a cylindrical barrel 209, thebarrel being a tight leak-free fit within the bore. A piston 210 havingtrunk extension 211 of slightly reduced diameter is slidably arrangedwithin the barrel 209 to define a space 212, constituting a fuel supplychamber, between the upper end of the trunk extension and the valve 204.A compression spring 213 encircling the trunk extension 211 biases thepiston 210 towards its lowermost position. Fuel is admitted to thesupply chamber 212 through a port 214 in the barrel 203, the portcommunicating with a supply inlet via a passage 215.

Also located within the cylindrical bore 203 is a second barrel 216,this also being a tight leak-free fit in the bore. The bottom end of thepiston 210 is castellated so that, as it is biassed downwardly by thespring 213, a space 219 remains beneath the piston for the admission ofhydraulic fluid.

A piston valve 220, which is a low clearance running fit in the barrel216, is biassed upwardly by a spring 221, the piston valve having aflange 222 against which the spring bears. Upward and downward movementsof the piston valve 220 are limited by engagement of the flange 222 witha step 233 in the barrel 216, and with a sleeve member 224,respectively. The piston valve 220 is provided for the purpose ofallowing rapid egress of used oil from the space 219 through an internalpassage 225 of the valve. The passage 225 communicates via radial holes226 with a shallow annular space 227' near the upper end of the valve.When the valve is in its upper position, the annular space 227communicates with the space 219 and permits oil egress, and when thevalve is in its lower position, the annular space 227 is isolated fromthe space 219. Thus the valve is closed in its lower position and openin its upper position.

The spring 221 is weaker, in terms of simple force, than the spring 213.However, in relation to the cross sectional areas of the piston valve220 and piston 210, respectively against which the springs act, thespring 221 is the stronger of the two. When therefore the piston 210 ismoving outwards to expel the spent oil in space 219, the piston valve220 will be open; but when the castellated end of the piston 210 reachesthe inwardly extended end of the piston valve 220, the latter will cedeand close. Thereafter introduction of high pressure oil into the space219 will oppose the piston 210 and move it upwards, while simultaneouslyit will keep the piston valve 220 closed down.

In practice a very small leakage of oil from the space 219 is requiredwhen the piston valve 220 is closed, and for this purpose the upper endof the piston valve may contain a small longitudinal channel ofappropriate cross section.

Any leakage of oil intothe annular space between the piston extension211 and the inner surface of the barrel 209 can pass out through a smallhole 228 and a oneway valve consisting of an O-ring 229 located in anannular groove in the outer surface of the barrel 209.

A screw threaded hole 231 in the metal body 202 communicating with thepassage 215 is adapted to receive a connector valve 232 (FIG. 26)whereby fuel is admitted to the passage 215 and thence to the supplychamber 212 via the port 214. The connector valve 232 comprises a valvebody having a first stemp portion 233, which is adapted to be screwedinto the hole 231, a second stem portion to which a fuel supply line maybe connected, and a flange 234 which is adapted to bear against the fuelinjector body 202. Within the valve body is a valve member 235 biassedtowards its closed position by a spring 236.

The fuel injector body 202 is also formed with a second cylindrical bore237, housing a barrel 238 which is a tight stationary leak-free fitwithin the bore. Mounted within the barrel 238 is a spring-loadedshuttle valve 239, to which is connected a downwardly extending hollowrod 240. A carrier cup 242 is free to move axially to and fro in asleeve 248. A compression spring 241 contained within the carrier cup242 acts upon the rod 240 to urge the shuttle valve 239 to its uppermostposition, at which position the valve lies very close to, but is spacedfrom, the machined outer surface of the engine cylinder 101. The upperlimiting position of the shuttle valve 239 is determined by the abutmentof the carrier cup 242 against a flange 243 of a third barrel 244, thediameter of the flange 243 ensuring a tight leak-free fit in the fuelinjector body 202. A central hole 245 in the top of the carrier cup 242is aligned with the hollow rod 240 for receiving oil which leaks downthe rod, this oil passing via a port 246 to the drainage passage 218.Downward movement of the carrier cup 242 is limited by a step 247 on theinner surface of the sleeve 248.

Means are provided to ensure that the port 246 remains in line with thecorresponding hole in the fuel injector body 202, so that leakage oilmay pass freely to the passage 218. The flange 243 is kept firmly lockedagainst its seat in the body 202 by a screw 251, acting through thesleeve 248. A seal 299 is fitted round the top of the barrel 238 toprevent leakage of cylinder gas.

A passage 249 in the engine cylinder extends from the cylinder space S(FIG. 18) to the space immediately above the shuttle valve 239, so thatthe latter is exposed to cylinder gas pressure and will be caused tomove downwardly in the barrel 238 when the gas pressure exceeds a valuedetermined by the force exerted on the shuttle valve by the spring 241.The force exerted by the spring 241, and hence the value of cylinderpressure at which the shuttle valve is moved downwards, can bepre-adjusted by any suitable means, such as an adjustable screw plug250, located in the bottom end of the retaining screw 251.

The upper end of the barrel 244 is of reduced diameter so as to be atight leak-free fit in a recess machined into the lower end of thebarrel 238.

1. A power unit of the type comprising an internal combustion enginehaving a pair of opposed free pistons working in a common cylinder, apair of pump units connected to the cylinder at opposite ends thereof,each pump unit comprising a pump piston coacting with a respective oneof the engine pistons and working in a pump chamber, the engine cylinderproviding inlet ports and exhaust ports communicating with respectiveinlet and exhaust manifolds for admitting combustion air to, andexhausting combustion gases from, the cylinder, the engine cylinderfurther providing first and second air compression spaces locatedrespectively behind the engine pistons, each air compression spacehaving a valve controlled air inlet and a valve controlled air outlet,and duct means connecting said air outlets with the inlet manifoldwherein the air compression spaces are separated from the pump chambersby bulkheads providing cylindrical openings through which the pumppistons extend, each opening being formed with a drainage grooveencircling the pump piston to provide a trap for leakage fluid, thegrooves being connected by ducts to a float chamber having afloat-controlled outlet, and means for biasing the float according tothe average air pressure in said air compression spaces.
 2. A power unitaccording to claim 1, wherein the float chamber provides an air spaceabove the float, which air space is connected to the air compressionspaces by a duct having a flow restricting orifice.